Alternative to Determine Algal Assemblages in Large Shallow Eutrophic Lake?

Pigment-based chemotaxonomy and CHEMTAX software have proven to be a valuable phytoplankton monitoring tool in marine environments, but are yet underdeveloped to deter-mine algal assemblages in freshwater ecosystems. The main objectives of this study were (1) to compare the results of direct microscopy and CHEMTAX in describing phytoplankton community composition dynamics in a large, shallow and eutrophic lake; (2) to analyze the efficiency of the pigment-based method to detect changes in phytoplankton seasonal dy-namics and during rapid bloom periods; (3) to assess the suitability of specific marker pig-ments and available marker pigment:chlorophyll a ratios to follow seasonal changes in eutrophic freshwater environment. A 5-year (2009-2013) parallel phytoplankton assess-ment by direct microscopy and by CHEMTAX was conducted using published marker pig-ment:chlorophyll a ratios. Despite displaying some differences from microscopy results, the pigment-based method successfully described the overall pattern of phytoplankton commu-nity dynamics during seasonal cycle in a eutrophic lake. Good agreement between the methods was achieved for most phytoplankton groups- cyanobacteria, chlorophytes, dia-toms and cryptophytes. The agreement was poor in case of chrysophytes and dinoflagel-lates. Our study shows clearly that published marker pigment:chlorophyll a ratios can be used to describe algal class abundances, but they need to be calibrated for specific fresh-water environment. Broader use of this method would enable to expand monitoring net-works and increase measurement frequencies of freshwater ecosystems to meet the goals of the Water Framework Directive